This invention relates to an improved process for removing ionic impurities from a sugar-containing solution, especially a high fructose corn syrup, by contacting the solution with specific ion exchange resins.
The preparation of a sugar-containing solution requires the removal of various impurities from the process streams. The main impurities in sugar are measured as sulphated ash which contains cations and anions such as Ca.sup.++, Mg.sup.++, Na.sup.+, K.sup.+, SO.sub.3.sup.--, Cl.sup.-, SO.sub.4.sup.-- and the like. For the production of a refined sugar-containing solution, it is necessary to remove these impurities. This is achieved by a demineralization process. It is standard practice in the demineralization process to pass the sugar solution first through a strongly acidic cation exchange resin in the hydrogen form, followed by passage through a strongly basic anion exchanger and/or weakly basic anion exchanger in the hydroxide or free base form. Once the ion exchange resins become nearly exhausted, it becomes necessary to regenerate their ion exchanging capacity. Prior to contacting the ion exchange resin with the regenerating agent, it is necessary to remove essentially all of the sugar solution from the resin bed. This is accomplished by passing effective quantities of water over the resin in order to "sweeten-off" the sugar solution within the resin bed. The resulting effluent is known in the industry as sweet-water.
The "sweetening-off" water or "sweet-water" after having sweetened-off the sugar from the resin contains an amount of recoverable sugar. The sweet-water is desirably recycled back as a dilution medium to other process steps (i.e., high fructose corn syrup saccharification). Typically, there is substantially more sweet-water generated than can be utilized for dilution purposes. Also, the sweet-water composition limits the usefulness of the sweet-water as a dilution source (e.g., high fructose sweet-water is not added back to the dextrose solution at the saccharification step). The excess sweet-water normally requires concentrating during some step in the refining process. This is accomplished by removing a substantial portion of the water without removing any of the sugar which has been washed off of the resin. This is generally accomplished by evaporating off an amount of water which results in a desired dissolved solids content, i.e., sugar content, in the unevaporated sweet-water.
The evaporation of the water is an expensive unit operation in the process for preparing refined sugars. Therefore, it is desirable to reduce the expense incurred during the evaporation operation of the process without detrimentally affecting the quality of sugar which is produced by the process. It is also desirable to increase the operating capacity of the resins for demineralizing a sugar-containing solution.